A "frog" is a component of track work used to allow one rail line to intersect and cross another rail line. A frog is typically supplied as an assembly of a casting which includes the point of frog, and heel and toe rails which are attached to the casting. The frog is inserted between intersecting rail lines by attaching the heel and toe rails of the frog assembly to the running rails of the intersecting rail lines.
It is a known feature of frogs that they are subjected to very high stresses, including notably stresses on the casting resulting from the impact of the wheels. This tends to wear and ultimately damage the castings. Accordingly it is desirable to use materials in the casting which are capable of withstanding the stresses involved. Manganese steel alloy is an example of a material widely used for this purpose because of its high degree of hardness and its ability to resist wear and impact damage. However the cost of manganese is high resulting in a relatively high cost of manufacturing frogs using manganese steel castings. In addition, while the use of manganese extends the life of the casting, it is still subject to impact damage and eventual wear.
We turn to consider various types of frogs and the steps that have been taken to try to minimize impact damage, maintenance requirements and costs of the frogs.
A common type of frog is known as the Rail Bound Manganese ("RBM") frog. The RBM is characterized by a casting of manganese steel alloy, heel and wing rails attached to the casting, spacer blocks and other components. The components of the frog are mechanically attached to one another and to base elements by means of a number of rail bolts and other fastening elements.
The heel end of an RBM casting is joined to heel rails by a mechanical connection. The connection is achieved by sandwiching the heel extension of the casting between the webs of a pair of heel rails, and by inserting a bolt transversely through the heel extension and the webs of the heel rails. This mechanical connection sometimes results in only a small gap between the heel end of the casting and the heel rails, but a small gap is sufficient to cause non-negligible impact damage when the wheels of the train pass over the gap. Even where an attempt is made to ensure a tight mechanical connection so as to minimize the gap, the weight of the train nonetheless causes relative vertical movement between the heel extension and the heel rails thereby creating a ridge against which the wheels of the train impact.
Flash butt welding is not a practical option for eliminating the gap or the relative movement of the components. Flash butt welding would induce arcing between the casting and the pair of heel rails. In any event, flash butt welding would be very difficult because of the geometry of the connection between the heel extension and the heel rails in an RBM type of frog. As a result of the mechanical connection between the heel extension and the heel rails in an RBM frog, damage occurs to the casting and the casting has a relatively short life span requiring replacement of the frogs. RBM frogs also include a number of rail bolts along the length of the frogs, and such rail bolts tend to break with wear. As a result, RBM frogs also require periodic maintenance for the replacement of broken bolts.
In an attempt to avoid the impact damage resulting from the mechanical connection between the casting and the heel rails, a frog known as the welded heel manganese ("WHM") frog was developed. In the WHM, the mechanical joint which would normally be found between the heel end of the casting and the heel rails is eliminated and replaced with a flash butt weld. This is made possible by creating a specially formed heel rail assembly which includes a flat end suitable to be flash butt welded to the casting.
The specially formed heel rail assembly of a WHM frog is created by machining one side of two heel rails so that they each present a flat vertical side extending a short distance along the rails. The two resulting flat surfaces are brought together and welded into a solid assembly. The merged ends of the heel rails are then machined flat. Because the heel rail assembly now presents a flat end, it can be flash butt welded to the end of the casting. This avoids the need for a long heel extension on the casting and allows the casting to be terminated much closer to the point of frog. As a result, a WHM insert can be cast shorter than an RBM insert, thereby using less manganese and reducing costs, in addition to eliminating a mechanical joint between the heel rails and the casting.
The welding of the end sections of the heel rails in the construction of a WHM heel rail assembly is typically done by means of sub-arc welding (the elements to be welded are submerged in sand). However, it appears that sub-arc welding may introduce defects into the heel rail assembly thereby subjecting the assembly to failure in the field. The WHM also suffers from the disadvantage of still requiring mechanical connection to the wing rails, base and other components associated with the frog, thereby requiring on-going maintenance.
An alternative to the RBM and WHM frogs for smaller angles of frogs is the Jointless Boltless Manganese ("JBM") frog. The overall JBM frog assembly is designed to occupy precisely the same footprint as an RBM assembly having the same angle of frog. However, the JBM insert is larger than the RBM insert and the wing rails and other components which would normally be found in the RBM or the WHM are integrally formed with the casting. The JBM insert is also longer than a WHM insert and encompasses what would be a substantial portion of the heel rail assembly of a WHM frog.
In a JBM frog, flash butt welding is used to connect the heel rails and toe rails to the casting. The JBM frog includes substantially no mechanical joints and no bolts other than those associated with spacer blocks used between the two heel rails and the two toe rails. As a result, the JBM frog requires very little maintenance. However, manganese is an expensive alloy and the JBM uses a relatively greater quantity of manganese than the RBM or the WHM. In addition, there are practical limits on the size of casting which may be cast by most foundries.
A shorter length of casting suggests that the rails will be closer together at the point at which they attach to the frog. It is generally thought not to be possible to effectively attach the rails to the inserts unless there is a distance of at least several inches between the centers of the heads of the rails. Attempts to attach rails closer together are defeated by abutment of the base of the rails against one another thereby limiting the extent to which they can be brought closely parallel. In addition, in the case of welding, the slag and other upset material produced can not effectively be removed from the weld area due to the inability to introduce the pneumatic chisel or other device in the area between the webs of the adjacent rails.
It is therefore an object of this invention to allow rails to be welded to the insert in closer proximity than has heretofore been possible in the prior art.
It is also an objective of the present invention to provide a frog which minimizes the number of mechanical joints.
It a further objective of the invention to allow the casting to be welded to the heel and toe rails rather than being mechanically connected as in the case of the RBM style of frogs.
It is another objective of the invention to eliminate the problems associated with sub-arc welding of the heel rail assembly in the WHM style of frogs.
It is also an objective of the present invention to have a casting which is shorter and which increases the range of angles of frog which can be achieved as compared to the JBM style of frog.